This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 Excerpt: ...wire so fine is only obtained by thickly coating an ordinary size of platinum wire with silver, FlG 44._View of Loop of and then drawing down Sensitive Fine Wire Un. der Microscope, the thick composite wire through successively diminishing dies. As the silver wire gets thinner and longer, so also does the internally ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 Excerpt: ...wire so fine is only obtained by thickly coating an ordinary size of platinum wire with silver, FlG 44._View of Loop of and then drawing down Sensitive Fine Wire Un. der Microscope, the thick composite wire through successively diminishing dies. As the silver wire gets thinner and longer, so also does the internally held wick or filament of platinum. After the little V loop of silver candle-wire has been soldered to the brass plates at B and D, Fig. 42, the device is carefully lowered into a bath of nitric acid, in such a manner that the point of the V loop is submerged in the acid, which immediately attacks and dissolves the silver chemically, leaving the platinum wick uninjured. The process is aided by a feeble electric current from a local voltaic cell, is watched under the microscope, and is arrested at the proper stage. The appearance in the microscope of the V loop after the silver has been dissolved off the tip is shown in Fig. 44, where A B and C D are the 76-micron or 0.076 millimeter silver wires, and e f g the 1.5 micron platinum filament, hanging in a short loop. The device is then ready for use and is conveniently protected from injury by placing it in a short glass bottle or test-tube. The connection of the little hot-wire device with the receiving antenna is illustrated in its simplest elements at Fig. 45. A B is the antenna, connected to ground through the hot-wire at H. A local voltaic circuit, in broken lines, connects a feeble electromotive force, such as a single voltaic cell, through the telephone receiver T and the hot-wire H. Prior to the advent of electromagnetic waves, a steady current flows through the local voltaic circuit, producing no sound in the receiver T. This current serves to warm the fine platinum wire, the electric resis...
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